Effect of welding on the fatigue strength of welded joints using the GMAW process in transformation induced plasticity s
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Effect of welding on the fatigue strength of welded joints using the GMAW process in transformation induced plasticity steels (TRIP) used in the automotive industry Victor Lopez1; Arturo Reyes1; Patricia Zambrano2; Joaquín Del Prado3 1
Corporación Mexicana de Investigación en Materiales, Ciencia y Tecnología 790 Saltillo, Coahuila, México. 2 Universidad Autónoma de Nuevo León, Ave. Universidad, San Nicolás, Nuevo León, México 3 METALSA, Carretera Miguel Aleman Km. 16.5, Apodaca N.L. México ABSTRACT Welding of TRIP steels are one of the technical challenges in the successful application of AHSS in chassis structures. Gas Metal Arc Welding (GMAW) is a common welding process used in the automotive industry, for joining mild steels. TRIP steel; however, do not offer the same ease of welding, and process control welding parameters is more critical. The welding parameters window represents the range of acceptable process parameters, primarily control of heat inputs, to obtain an acceptable weld. As a result, the effects of the heat input variations are greater and TRIP steel has a narrower welding parameters window in which acceptable welds can be made. Mechanical properties of the lap joints of TRIP 780 steel 2.8 mm thickness was analyzed, fusion welds were evaluated using fatigue tests on these joints for different heat inputs. Fatigue testing was conducted under a different number of nominal stress ranges to obtain the S/N curves of the weld joints. Keywords: Fatigue, Welding, Steel INTRODUCTION Due to high demand for energy saving, safety and emission reduction, Advanced High Strength Steels (AHSS) have become very attractive materials for automotive industry, especially when the performance of the welded structures is required. Gas Metal Arc Welding (GMAW) is a common welding process used in the automotive industry, for joining mild steels, where it is recognized for its quality and speed. TRIP steel; however, do not offer the same ease of welding, and process control welding parameters is more critical. The welding parameters window represents the range of acceptable process parameters, primarily control of heat inputs, to obtain an acceptable weld. TRIP steel differ from mild steels in chemical composition and thermal processing, resulting in a different microstructure; designed with a high chemistry to have higher strength at equivalent thickness compared to mild steels. As a result, the effects of the heat input variations are greater and TRIP steel has a narrower welding parameters window in which acceptable welds can be made. GMAW welding parameters for lap joints of this steel were developed in order to obtain different heat inputs. Mechanical and Metallurgical properties of the lap joints of TRIP 780 steel 2.8 mm thickness was analyzed fusion welds were evaluated using fatigue tests on these joints for different heat inputs. Fatigue testing was conducted under a different number of nominal stress ranges to obtain the S/N curves of the weld joints .Variations in weld parameters influence the joint performance
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